Alignment marks in substrate having through-substrate via (TSV)

ABSTRACT

A device includes a substrate, and an alignment mark including a conductive through-substrate via (TSV) penetrating through the substrate.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No. 12/874,952, entitled “Alignment Marks in Substrate Having Through-Substrate Via (TSV),” filed on Sep. 2, 2010, which application is incorporated herein by reference.

BACKGROUND

In order to form three-dimensional (3D) integrated circuit structures, through-substrate vias (TSVs) are used to electrically couple front-side features to the backside features of a wafer. On the front side, there may be interconnect structures and metal bumps, for example. On the backside, there may be metal bumps and redistribution lines. Dual-side alignment needs to be performed in order to accurately align the backside features and the front-side features with each other.

Typically, the front-side features are formed on the wafer first, followed by a backside grinding to thin a silicon substrate in the wafer, until the TSVs are exposed. Front-side alignment marks are incorporated in the front-side features. The dual-side alignment is performed from the backside using an infra-red (IR) alignment system for locating the front-side alignment marks, wherein the infra-red light emitted by the IR alignment system penetrates through the thinned silicon substrate to reach the front-side alignment marks. Backside alignment marks are then made on the backside of the wafers by etching into the backside layer(s) and into the silicon substrate.

Due to the limitation of the IR alignment system, and further due to the thickness variation in the grinded silicon substrate, the accuracy of the dual-side alignment is low, and the misalignment may be as high as about 2 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIGS. 1 through 7 are cross-sectional views of intermediate stages in the manufacturing and using of alignment marks in accordance with an embodiment;

FIG. 8 illustrates a top view of a front-side alignment mark;

FIGS. 9A through 9G illustrate various alignment marks formed of through-substrate vias (TSVs);

FIG. 10 illustrates a lithography mask for forming the TSVs; and

FIGS. 11A through 11D illustrate various alignment marks formed of trench-type TSVs.

DETAILED DESCRIPTION

The making and using of the embodiments of the disclosure are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative, and do not limit the scope of the disclosure.

A novel dual-side alignment mark and methods of forming the same are provided in accordance with an embodiment. The intermediate stages of manufacturing the dual-side alignment marks are illustrated in accordance with an embodiment. The variations of the embodiments are then discussed. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

Referring to FIG. 1, wafer 2, which includes substrate 10, is provided. In an embodiment, substrate 10 is a semiconductor substrate, such as a bulk silicon substrate, although it may include other semiconductor materials such as group III, group IV, and/or group V elements. Integrated circuit devices 16, which may include transistors, may be formed at front surface 10 a of substrate 10. In alternative embodiments, wafer 2 is an interposer or a package substrate, which may not include active devices such as transistors therein. However, passive devices such as transistors and capacitors may be included in wafer 2. Substrate 10 thus may be formed of a semiconductor material such as silicon or formed of a dielectric material. Interconnect structure 12 including metal lines and vias formed therein is formed over substrate 10, and may be electrically coupled to the integrated circuit devices. The metal lines and vias may be formed of copper or copper alloys, and may be formed using the well-known damascene processes. Interconnect structure 12 may include commonly known inter-layer dielectric (ILD) 11 and inter-metal dielectrics (IMDs), which are formed over ILD 11.

Alignment mark 14 is formed on the front side of substrate 10, and may be formed, for example, in the first-level metal layer (the bottom IMD layer), although it may be formed in other-level metal layers. A top view of an exemplary alignment mark 14 is illustrated in FIG. 8. Alignment mark 14 may have different shapes other than what is shown in FIG. 8.

Through-substrate vias (TSVs) 20 are formed in substrate 10, and extend from front surface 10 a of substrate 10 into substrate 10. Depending on whether TSVs 20 are formed using a via-first approach or a via-last approach, TSVs 20 may extend into ILD 11 that is used to cover the active devices, but not into the IMD layers in interconnect structure 12. Alternatively, TSVs 20 may penetrate through both substrate 10, ILD 11, and possibly interconnect structure 12. Isolation layers 22 are formed on the sidewalls of TSVs 20, and electrically insulate the respective TSVs 20 from substrate 10. Isolation layers 22 may be formed of commonly used dielectric materials such as silicon nitride, silicon oxide (for example, tetra-ethyl-ortho-silicate (TEOS) oxide), and the like.

TSVs 20 include functional TSVs 20A and alignment-mark TSVs 20B. Although only one alignment-mark TSV 20B is illustrated, there may be a plurality of alignment-mark TSVs 20B, as illustrated in FIGS. 9A through 9G and FIGS. 11A through 11D. Functional TSVs 20A may be used to electrically couple the conductive features on the front side of substrate 10 to the conductive features on the backside of substrate 10. Alignment-mark TSVs 20B are used for aligning the features on the backside to the features on the front side of wafer 2. Alignment-mark TSVs 20B and alignment mark 14 are aligned to each other. In an embodiment, functional TSVs 20A and alignment-mark TSVs 20B are formed simultaneously. In alternative embodiments, functional TSVs 20A and alignment-mark TSVs 20B are formed at different times by separate formation processes. Further, functional TSVs 20A may have a same diameter, a same pitch, and/or a same height as alignment-mark TSVs 20B. Alternatively, the diameter, the pitch, and/or the height of functional TSVs 20A may be different from that of alignment-mark TSVs 20B. Metal bumps 18 may then be formed on the front side of wafer 2.

Referring to FIG. 2, wafer 2 is bonded to carrier 27, for example, through adhesive 25, which may be ultra-violet (UV) glue. Next, as shown in FIG. 3, a backside grinding is performed to remove excess portions of substrate 10. An etch may further be performed to lower back surface 10 b of substrate 10, so that TSVs 20 protrude above back surface 10 b.

In FIG. 4, passivation layer 24 is formed to cover back surface 10 b of substrate 10 and TSVs 20. In an exemplary embodiment, passivation layer 24 includes silicon nitride layer 24 a and silicon oxynitride layer 24 b over silicon nitride layer 24 a, although passivation layer 24 may be formed different materials and/or have different structures.

Next, using a patterned photo resist, portions of passivation layer 24 are etched, and the ends of TSVs 20 (including functional TSVs 20A and alignment-mark TSVs 20B) are exposed. The patterned photo resist is then removed, resulted in a structure shown in FIG. 5. The exposed alignment-mark TSVs 20B may thus be used as alignment mark 32, which are used for the alignment in the formation of backside features such as RDLs and/or metal bumps, so that the backside features on the backside of wafer 2 may be accurately aligned to desirable positions, and aligned to front-side alignment mark 14.

FIG. 6 illustrates the formation of under-bump metallurgy (UBM) layer 28, which may be blanket formed on passivation layer 24 and exposed TSVs 20, for example. UBM layer 28 may be formed using sputtering or other applicable methods. UBM layer 28 may include a barrier layer 28 a and a seed layer 28 b on barrier layer 28 a. In some embodiments, barrier layer 28 a includes a Ti layer, a Ta layer, a TiN layer, a TaN layer, or combinations thereof, although other materials may also be used. In some embodiments, the seed layer 28 b includes copper.

FIG. 7 illustrates the formation of exemplary backside features on the backside of wafer, wherein the backside features may include metal layers, metal bumps, passivation layers, micro bumps, and/or the like. In the exemplary embodiment as shown in FIG. 7, backside features 30 represent metal bumps and/or redistribution lines (RDLs). It is appreciated that although one layer of metal bumps/RDLs is shown, there may be one or more layer of RDLs, and metal bumps over and connected to the RDLs. In an exemplary embodiment, the formation of features 30 includes forming a mask (not shown) over UBM layer 28, with a portion of UBM layer 28 exposed through openings in the mask. A plating is then performed to plate a conductive material into the openings to form backside features 30. The mask is then removed, and the portions of the UBM layer 28 previously covered by the mask are etched. Alignment-mark TSVs 20B are also exposed, and may be used for the alignment in the formation of additional features such as RDLs and/or metal bumps over backside features 30.

FIGS. 9E through 9G illustrate top views of exemplary alignment marks 32, each formed of a plurality of alignment-mark TSVs 20B. When the plurality of alignment-mark TSVs 20B are grouped to form alignment mark 32, the plurality of alignment-mark TSVs 20B may be arranged in an rectangular region (also marked as 32) having length L and width W, wherein the rectangular region may be free from functional TSVs. Length L and width W may be between about 50 μm and about 400 μm, and may be between about 100 μm and about 200 μm. Accordingly, the rectangular region may have a top-view area smaller than about 400 μm×400 μm, or less than about 200 μm×200 μm.

In FIGS. 9A through 9G, alignment-mark TSVs 20B may be arranged as different patterns. For example, in FIGS. 9A and 9F, alignment-mark TSVs 20B are aligned to lines 36A and 36B that cross each other. In FIGS. 9B, 9C, and 9G, alignment-mark TSVs 20B are aligned to lines 38A and 38B that terminate at common points 40. FIGS. 9D and 9E illustrate other exemplary patterns.

FIG. 10 illustrates an exemplary lithography mask 33 for forming TSVs 20, wherein alignment mark patterns 32′ are formed in lithography mask 33 along with patterns 20A′ for forming functional TSVs 20. Alignment-mark patterns 32′ define the patterns of alignment-mark TSVs 20B, while patterns 20A′ define the patterns of functional TSVs 20A.

FIGS. 11A through 11D illustrate alternative embodiments in which alignment marks 32 are formed of trench-type TSVs 20B, which, instead of having circular top-view shapes, may have other shapes including, but are not limited to, rectangles, crosses, and combinations thereof. Trench-type TSVs 20B may be formed at the same time as, or at different times than, forming functional TSVs 20A. Similarly, trench-type TSVs 20B also penetrate through substrate 10.

By using the embodiments, alignment marks may be formed at the same time functional TSVs are formed. Therefore, the cost incurred in conventional alignment-mark formation processes, including forming a photo resist for defining the patterns of backside alignment marks on the backside of wafer 2, etching wafer 2 for forming the backside alignment marks, and stripping off the photo resist is saved. Further, the accuracy for forming the alignment marks is improved. In conventional alignment mark formation techniques, the misalignment may be as great as about 2 μm. While in the embodiments, the misalignment is reduced to less than 1 μm.

Features in accordance with embodiments include a substrate, and an alignment mark including a conductive TSV penetrating through the substrate.

Features in accordance with further embodiments include a semiconductor substrate having a front surface and a back surface; a functional TSV penetrating through the semiconductor substrate; an active device on a front side of the semiconductor substrate; an interconnect structure including a plurality of metal layers on the front side of the semiconductor substrate; a dielectric layer contacting a back surface of the semiconductor substrate; and an alignment mark including a plurality of TSVs. The plurality of TSVs penetrates through the semiconductor substrate and the dielectric layer, wherein no redistribution line and metal bump is on a back side of the semiconductor substrate and electrically coupled to the plurality of TSVs.

Features in accordance with embodiments include a semiconductor substrate having a front surface and a back surface; a functional TSV in the semiconductor substrate and extending from the front surface to the back surface; an interconnect structure including a plurality of metal layers on a front side of the semiconductor substrate; an alignment mark on the front side of the semiconductor substrate; a dielectric layer contacting the back surface of the semiconductor substrate; and a plurality of TSVs penetrating through the semiconductor substrate. No redistribution line and metal bump is formed on a backside of the semiconductor substrate and electrically coupled to the plurality of TSVs.

Features in accordance with embodiments include providing a substrate; forming a first and a second conductive TSV in the substrate; and forming a conductive feature on a backside of the substrate and electrically coupled to the second conductive TSV. The step of forming the conductive feature is performed using the first conductive TSV as an alignment mark. No additional conductive feature is formed to electrically couple to the first conductive TSV and at a same level as the conductive feature.

Features in accordance with embodiments include providing a substrate; forming a functional TSV and a plurality of TSVs in the substrate, wherein the plurality of TSVs are grouped to form an alignment mark; forming an interconnect structure on a front side of the substrate; grinding a backside of the substrate until the functional TSV and the alignment mark are exposed; forming a dielectric layer contacting a back surface of the substrate, the functional TSV, and the alignment mark; etching the dielectric layer to expose the functional TSV and the alignment mark; forming an under-bump-metallurgy (UBM) layer to cover the dielectric layer and to contact the functional TSV and the alignment mark; and forming a conductive feature directly over and electrically coupled to the functional TSV, wherein the step of forming the conductive feature is performed using the alignment mark for alignment.

Although the embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. In addition, each claim constitutes a separate embodiment, and the combination of various claims and embodiments are within the scope of the disclosure. 

What is claimed is:
 1. A method comprising: performing a backside grinding on a substrate to expose an alignment through-substrate via (TSV) and a function TSV, wherein a back surface of the substrate is exposed after the backside grinding, the alignment TSV formed from three or more straight conductive segments in a plan view; forming a passivation layer contacting the back surface, wherein the passivation layer is formed as a blanket layer, and wherein the alignment and the functional TSVs penetrate through the passivation layer; and forming a conductive feature on a backside of the substrate, wherein the conductive feature is electrically coupled to the functional TSV, and the forming the conductive feature is performed using the alignment TSV as an alignment mark, wherein the alignment TSV and the functional TSV are a same width.
 2. The method of claim 1 further comprising forming the alignment and the functional TSVs comprising: etching the back surface of the substrate, with ends of the alignment and the functional TSVs protruding beyond the back surface of the substrate, wherein a space is left by an etched back surface layer of the substrate, and the passivation layer is filled into the space; and removing portions of the passivation layer that overlap the alignment and the functional TSVs to expose the alignment and the functional TSVs.
 3. The method of claim 1, wherein the forming the conductive feature comprises forming a redistribution line.
 4. The method of claim 1, wherein when the conductive feature is formed, no conductive feature is formed to electrically couple to the alignment TSV.
 5. The method of claim 1 further comprising forming an additional alignment mark on a front side of, and outside of, the substrate, wherein a position of the alignment TSV is aligned relative to the additional alignment mark, wherein the additional alignment mark is different from the alignment TSV.
 6. The method of claim 1 further comprising forming an interconnect structure on a front side of the substrate, wherein no conductive feature in the interconnect structure is electrically coupled to the alignment TSV.
 7. The method of claim 1, wherein the substrate comprises: a front surface opposite to the back surface of the substrate, with the back surface on the backside; and a transistor is formed at the front surface of the substrate.
 8. The method of claim 1, wherein when the alignment TSV is used as the alignment mark, the back surface of the substrate is covered by the passivation layer.
 9. A method comprising: forming a first conductive through-substrate via (TSV) and a second conductive TSV in a substrate, the substrate having a front side and a backside, the first conductive TSV having a first width in a direction parallel to the backside, the second TSV having a second width in the direction parallel to the backside, the second width equal to the first width; forming an interconnect structure on the front side of the substrate, wherein the second TSV in the substrate is electrically coupled to metal lines and vias in the interconnect structure, and no metal line and via in the interconnect structure is electrically coupled to the first conductive TSV in the substrate; performing a backside grinding on the substrate to expose the first conductive TSV and the second conductive TSV, wherein the backside grinding is performed from the backside of the substrate; forming a passivation layer over a back surface of the substrate, the first conductive TSV and the second conductive TSV penetrating through the passivation layer; forming an under-bump metallurgy (UBM) layer on the passivation layer, the UBM layer being over the back surface of the substrate, the first conductive TSV, and the second conductive TSV; forming a conductive feature on the UBM layer, wherein the conductive feature is electrically coupled to the second conductive TSV, and wherein when the conductive feature is formed, a position of the conductive feature is determined using the first conductive TSV that penetrates through the passivation layer as an alignment mark, and wherein no conductive feature is formed to connect to the first conductive TSV; and removing portions of the UBM layer over the first conductive TSV and the back surface of the substrate.
 10. The method of claim 9, wherein the forming the conductive feature comprises forming a redistribution line.
 11. The method of claim 9, wherein the forming the conductive feature comprises forming a metal bump.
 12. The method of claim 9, wherein the substrate comprises a front surface and the back surface opposite to the front surface, with the back surface being on the backside of the substrate, wherein a transistor is formed at the front surface of the substrate.
 13. The method of claim 9 further comprising: etching the back surface of the substrate, with ends of the first and the second conductive TSVs protruding beyond the back surface of the substrate, wherein a space is left by an etched back surface layer of the substrate; forming the passivation layer on the back surface of the substrate, wherein the passivation layer is filled into the space; and removing portions of the passivation layer that overlap the first and the second conductive TSVs to expose the first and the second conductive TSVs.
 14. A method comprising: simultaneously forming a group of alignment through-substrate vias (TSVs) and a group of functional TSVs in a substrate, the group of alignment TSVs arranged in a rectangular region substantially free of each of the group of functional TSVs, each of the group of functional TSVs electrically coupling first conductive features on a back surface of the substrate to second conductive features on a front surface of the substrate; performing a backside grinding from a backside of the substrate, wherein the group of alignment TSVs and the group of functional TSVs are exposed through the back surface of the substrate; after the backside grinding, recessing the back surface of the substrate to allow the group of alignment TSVs and the group of functional TSVs to protrude beyond the back surface, wherein a space is left by an etched back surface layer of the substrate removed in the recessing; forming a passivation layer on the back surface of the substrate, wherein the passivation layer is filled into the space; removing portions of the passivation layer that overlap the group of alignment TSVs to expose the group of alignment TSVs; and with the passivation layer covering the back surface of the substrate, forming the first conductive features on the back surface of the substrate and electrically coupled to at least one TSV of the group of functional TSVs, with the group of alignment TSVs used as an alignment mark for positioning the first conductive features.
 15. The method of claim 14, wherein the first conductive features comprise at least one of a redistribution line and a metal bump.
 16. The method of claim 14, wherein no additional conductive feature is formed simultaneously as the first conductive features to electrically couple to the group of alignment TSVs.
 17. The method of claim 14 further comprising forming an interconnect structure on a front side of the substrate, wherein no conductive feature in the interconnect structure is electrically coupled to the group of alignment TSVs.
 18. The method of claim 14, wherein the substrate further comprises the front surface opposite to the back surface, wherein a transistor is formed at the front surface of the substrate.
 19. The method of claim 14, wherein when the group of alignment TSVs is used as the alignment mark, wherein the group of alignment TSVs is exposed through openings in the passivation layer. 